# Scheduling Control (A)


![left](./student-guide/diagram/25-Generate-speed-control-01-01.png)

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region-schedule-limit 
The number of tasks scheduled for the region at the same time
Default value: 2048

leader-schedule-limit
The number of tasks scheduled by the leader at the same time.
Default value: 4

replica-schedule-limit
The number of tasks that are scheduling replicas at the same time.
Default value: 64

merge-schedule-limit
For tasks scheduled by Region Merge at the same time, set to 0 to close Region Merge.
Default value: 8

hot-region-schedule-limit
Controls the concurrent hot region tasks. This configuration item is scheduled independently of Region.
Default value: 4

tolerant-size-ratio
 Controls the balance buffer size. When the difference between the scores of the leader or region of the two stores is less than the specified multiple of the region size, PD considers balance to be balanced at this point.
Default value: 0
Because the TiKV underlying storage engine uses RocksDB, size changes are not timely, so we introduced this parameter to reduce the impact of compaction on scheduling and avoid the problem of repeated scheduling. Before calculating the score, we will use this parameter to set a buffer, usually the size of the tolerant-size-ratio* region size. The main meaning is that if the score difference is within the buffer range, no scheduling will occur.